The contents of the references cited in the specification are hereby incorporated by reference.
Synthetically valuable 2-oxoalkylidenetriphenylphosphoranes (OATP) are usually prepared in two ways. Either by reaction of triphenylphosphine with .alpha.-haloketones and subsequent treatment of the resulting phosphonium salt with alkali metal hydroxide (M. I. Shevchuk et al., Zhurnal obshei Khimii, Vol. 40, N 1, pp. 48-57, 1970) ##STR3## (R=alkyl, aryl or alkoxy) or by acylation of methylenetriphenylphosphorane with acyl chlorides (H. J. Bestmann et al., Chem. Ber. 95, 1513, 1962) or reactive carboxyl derivatives (Y. Sheng et al., Synthesis, 1984, p. 924-926). EQU Ph.sub.3 P.dbd.CH.sub.2 +RCOX.fwdarw.Ph.sub.3 P.dbd.CH--COR
(R=alkyl, perfluoroalkyl or aryl; X=halogen, OR)
Some phosphorus ylides containing other stabilizing groups have been prepared by reaction of phenylethynyltriphenylphosphonium bromide (II) with anilines, enamines or acetoacetate (H. Hoffmann et al., Tetrahedron Letters N17, 1964, pp. 983-987) ##STR4## or by acylation of methylenetriphenylphosphorane with imidoyl chloride (H. Yoshida et al., Synthesis 1977, pp. 626-628). ##STR5## R.sup.1 (V).dbd.Ar; R.sup.2 (V).dbd.Ar, SAlk, OAlk
Some 2-thioxoalkylidenetriphenylphosphoranes (VII) have been prepared by alkylation of triphenylphosphine with thio derivatives (VI) (EP-A-052 931); ##STR6## M (VII).dbd.S; R.sup.1, R.sup.2 .dbd.H, Alk, Aryl
Except for the above mentioned processes, it has not been possible hitherto by the prior art to obtain phosphorus betaines having a stabilizing group other than the carbonyl oxygen in the .beta. position. Phenylethynyltriphenylphosphonium bromide (II), imidoyl chlorides (IV) and the alkylated (thio)carbonyl compounds are usually accessible with great difficulty, so that the preparation of phosphorus betaines containing the above mentioned groups should be limited to only a few examples.
On the other hand, substitution of the oxygen by other groups having different steric and electronic properties would be an expedient way to modify organic compounds.